During the next year we hope to characterize ecdysone binding proteins present in an embryonic cell line (Kc) established from Drosophila. The cell line has a defined response to beta-ecdysone. A similar response can be induced by alpha-ecdysone at a 100-fold increase in concentration. In addition, the cells do not metabolize ecdysone to a discernable extent. Characterization of the macromolecular binding components by conventional physical techniques will permit elucidation of the mechanism whereby ecdysone interacts with the Drosophila genome. BIBLIOGRAPHIC REFERENCES: Horn, D.H.S. Wilkie, J.S., Sage, B.A., and O'Connor, J.D., "A high affinity antiserum specific for the ecdysone nucleus." J. Insect Physiol., 22:901 (1976). Chang, E.S., Sage, B.A., and O'Connor, J.D., "The characterization of circulating ecdysone titers in the crab Pachygrapsus crassipes." Colloq. Int. Centre Nat. Rech. Sci., 251:263 1976.